Lithographic apparatus and a device manufacturing method

ABSTRACT

An immersion lithographic apparatus is disclosed that includes a fluid handling system configured to confine immersion liquid to a localized space between a final element of a projection system and a substrate and/or table and a gas supplying device configured to supply gas with a solubility in immersion liquid of greater than 5×10 −3  mol/kg at 20° C. and 1 atm total pressure to an area adjacent the space.

This application is a continuation of U.S. patent application Ser. No.12/961,586, filed Dec. 7, 2010, which claims priority and benefit under35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No.61/285,021, entitled “A Lithographic Apparatus and A DeviceManufacturing Method”, filed on Dec. 9, 2009, and to U.S. ProvisionalPatent Application Ser. No. 61/313,964, entitled “A LithographicApparatus and A Device Manufacturing Method”, filed on Mar. 15, 2010.The contents of those applications are incorporated herein in theirentirety by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device using a lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe invention will be described with reference to liquid. However,another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that must be accelerated during a scanningexposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion fluid is handled by a fluidhandling system, device structure or apparatus. In an embodiment thefluid handling system may supply immersion fluid and therefore be afluid supply system. In an embodiment the fluid handling system may atleast partly confine immersion fluid and thereby be a fluid confinementsystem. In an embodiment the fluid handling system may provide a barrierto immersion fluid and thereby be a barrier member, such as a fluidconfinement structure. In an embodiment the fluid handling system maycreate or use a flow of gas, for example to help in controlling the flowand/or the position of the immersion fluid. The flow of gas may form aseal to confine the immersion fluid so the fluid handling structure maybe referred to as a seal member; such a seal member may be a fluidconfinement structure. In an embodiment, immersion liquid is used as theimmersion fluid. In that case the fluid handling system may be a liquidhandling system. In reference to the aforementioned description,reference in this paragraph to a feature defined with respect to fluidmay be understood to include a feature defined with respect to liquid.

SUMMARY

If the immersion liquid is confined by a fluid handling system to alocalized area on the surface which is under the projection system, ameniscus extends between the fluid handling system and the surface. Ifthe meniscus collides with a droplet on the surface, this may result ininclusion of a bubble in the immersion liquid. The droplet may bepresent on the surface for various reasons, including because of leakingfrom the fluid handling system. A bubble in immersion liquid can lead toimaging errors, for example by interfering with a projection beam duringimaging of the substrate.

It is desirable, for example, to provide a lithographic apparatus inwhich the likelihood of bubble inclusion is at least reduced.

According to an aspect, there is provided an immersion lithographicapparatus comprising: a fluid handling system configured to confineimmersion liquid to a localized space between a final element of aprojection system and a substrate and/or table; and a gas supplyingdevice configured to supply gas with a solubility in the immersionliquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm total pressureto a region adjacent the space.

According to an aspect, there is provided an immersion lithographicapparatus comprising: a fluid handling system configured to confineimmersion liquid to a localized space between a final element of aprojection system and a substrate and/or table; and a gas supplyingdevice configured to supply gas with a diffusivity in the immersionliquid of greater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atm total pressureto a region adjacent the space.

According to an aspect, there is provided an immersion lithographicapparatus comprising: a fluid handling system configured to confineimmersion liquid to a localized space between a final element of aprojection system and a substrate and/or table; and a gas supplyingdevice configured to supply gas with a product of diffusivity andsolubility in the immersion liquid of greater than that of air at 20° C.and 1 atm total pressure to a region adjacent the space.

According to an aspect, there is provided a device manufacturing method,comprising projecting a patterned beam of radiation through an immersionliquid confined to a localized space between a final element of aprojection system and a substrate; and providing to a region adjacent tothe space a gas with a solubility in the immersion liquid of greaterthan 5×10⁻³ mol/kg at 20° C. and 1 atm total pressure.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a localized space between a final elementof a projection system and a substrate; and providing to a regionadjacent to the space a gas with a diffusivity in the immersion liquidof greater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atm total pressure.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a localized space between a final elementof a projection system and a substrate; and providing to a regionadjacent to the space a gas with a product of diffusivity and solubilityin the immersion liquid of greater than that of air at 20° C. and 1 atmtotal pressure.

According to an aspect, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table, and comprising agas supplying device configured to supply gas with a solubility in theimmersion liquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm totalpressure to a region adjacent the space.

According to an aspect, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table; and comprising agas supplying device configured to supply gas with a diffusivity in theimmersion liquid of greater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atmtotal pressure to a region adjacent the space.

According to an aspect, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table; and comprising agas supplying device configured to supply gas with a product ofdiffusivity and solubility in the immersion liquid of greater than thatof air at 20° C. and 1 atm total pressure to a region adjacent thespace.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 7 depicts, in plan, a liquid supply system for use in alithographic projection apparatus; and

FIG. 8 is a graph showing permittable bubble size versus scan speed.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device MA inaccordance with certain parameters;

a support table, e.g. a sensor table to support one or more sensors or asubstrate table WT constructed to hold a substrate (e.g. a resist-coatedsubstrate) W, connected to a second positioner PW configured toaccurately position the surface of the table, for example of a substrateW, in accordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling radiation.

The support structure MT holds the patterning device MA. It holds thepatterning device MA in a manner that depends on the orientation of thepatterning device MA, the design of the lithographic apparatus, andother conditions, such as for example whether or not the patterningdevice MA is held in a vacuum environment. The support structure MT canuse mechanical, vacuum, electrostatic or other clamping techniques tohold the patterning device MA. The support structure MT may be a frameor a table, for example, which may be fixed or movable as required. Thesupport structure MT may ensure that the patterning device MA is at adesired position, for example with respect to the projection system PS.Any use of the terms “reticle” or “mask” herein may be consideredsynonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device MA may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore tables, e.g., two or more substrate tables or a substrate table anda sensor table (and/or two or more patterning device tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source SO and the lithographic apparatus may beseparate entities, for example when the source SO is an excimer laser.In such cases, the source SO is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source SO may be an integral part of thelithographic apparatus, for example when the source SO is a mercurylamp. The source SO and the illuminator IL, together with the beamdelivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator IL can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator IL may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section. Similar to the source SO, the illuminator IL may or maynot be considered to form part of the lithographic apparatus. Forexample, the illuminator IL may be an integral part of the lithographicapparatus or may be a separate entity from the lithographic apparatus.In the latter case, the lithographic apparatus may be configured toallow the illuminator IL to be mounted thereon. Optionally, theilluminator IL is detachable and may be separately provided (forexample, by the lithographic apparatus manufacturer or anothersupplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions C (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam B is projected onto a target portion C at one time (i.e.a single static exposure). The substrate table WT is then shifted in theX and/or Y direction so that a different target portion C can beexposed. In step mode, the maximum size of the exposure field limits thesize of the target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam Bis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to thesupport structure MT may be determined by the (de-)magnification andimage reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in thenon-scanning direction) of the target portion C in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in the scanning direction) of the target portion C.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale, features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc.

Arrangements for providing liquid between a final element of theprojection system PS and the substrate can be classed into three generalcategories. These are the bath type arrangement, the so-called localizedimmersion system and the all-wet immersion system. In a bath typearrangement substantially the whole of the substrate W and optionallypart of the substrate table WT is submersed in a bath of liquid.

A localized immersion system uses a liquid supply system in which liquidis only provided to a localized area of the substrate. The space filledby liquid is smaller in plan than the top surface of the substrate andthe area filled with liquid remains substantially stationary relative tothe projection system PS while the substrate W moves underneath thatarea. FIGS. 2-7 show different supply devices which can be used in sucha system. A sealing feature is present to seal liquid to the localizedarea. One way which has been proposed to arrange for this is disclosedin PCT patent application publication no. WO 99/49504.

In an all wet arrangement the liquid is unconfined. The whole topsurface of the substrate and all or part of the substrate table iscovered in immersion liquid. The depth of the liquid covering at leastthe substrate is small. The liquid may be a film, such as a thin film,of liquid on the substrate. Immersion liquid may be supplied to or inthe region of a projection system and a facing surface facing theprojection system (such a facing surface may be the surface of asubstrate and/or a substrate table). Any of the liquid supply devices ofFIGS. 2-5 can also be used in such a system. However, a sealing featureis not present, not activated, not as efficient as normal or otherwiseineffective to seal liquid to only the localized area.

As illustrated in FIGS. 2 and 3, liquid is supplied by at least oneinlet onto the substrate, preferably along the direction of movement ofthe substrate relative to the final element. Liquid is removed by atleast one outlet after having passed under the projection system. As thesubstrate is scanned beneath the element in a −X direction, liquid issupplied at the +X side of the element and taken up at the −X side. FIG.2 shows the arrangement schematically in which liquid is supplied viainlet and is taken up on the other side of the element by outlet whichis connected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible; one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element. Note that the directionof flow of the liquid is shown by arrows in FIGS. 2 and 3.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletscan be arranged in a plate with a hole in its centre and through whichthe projection beam is projected. Liquid is supplied by one groove inleton one side of the projection system PS and removed by a plurality ofdiscrete outlets on the other side of the projection system PS, causinga flow of a thin film of liquid between the projection system PS and thesubstrate W. The choice of which combination of inlet and outlets to usecan depend on the direction of movement of the substrate W (the othercombination of inlet and outlets being inactive). Note that thedirection of flow of fluid and of the substrate is shown by arrows inFIG. 4.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement structure which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5.

FIG. 5 schematically depicts a localized liquid supply system or fluidhandling system with a liquid confinement structure 12, which extendsalong at least a part of a boundary of the space between the finalelement of the projection system and the substrate table WT or substrateW. (Please note that reference in the following text to surface of thesubstrate W also refers in addition or in the alternative to a surfaceof the substrate table, unless expressly stated otherwise.) The liquidconfinement structure 12 is substantially stationary relative to theprojection system in the XY plane though there may be some relativemovement in the Z direction (in the direction of the optical axis). Inan embodiment, a seal is formed between the liquid confinement structure12 and the surface of the substrate W and may be a contactless seal suchas a gas seal (such a system with a gas seal is disclosed in Europeanpatent application publication no. EP-A-1,420,298) or liquid seal.

The liquid confinement structure 12 at least partly contains liquid inthe space 11 between a final element of the projection system PS and thesubstrate W. A contactless seal 16 to the substrate W may be formedaround the image field of the projection system PS so that liquid isconfined within the space between the substrate W surface and the finalelement of the projection system PS. The space 11 is at least partlyformed by the liquid confinement structure 12 positioned below andsurrounding the final element of the projection system PS. Liquid isbrought into the space below the projection system PS and within theliquid confinement structure 12 by liquid inlet 13. The liquid may beremoved by liquid outlet 13. The liquid confinement structure 12 mayextend a little above the final element of the projection system. Theliquid level rises above the final element so that a buffer of liquid isprovided. In an embodiment, the liquid confinement structure 12 has aninner periphery that at the upper end closely conforms to the shape ofthe projection system or the final element thereof and may, e.g., beround. At the bottom, the inner periphery closely conforms to the shapeof the image field, e.g., rectangular, though this need not be the case.

The liquid may be contained in the space 11 by a gas seal 16 which,during use, is formed between the bottom of the barrier member 12 andthe surface of the substrate W. The gas seal is formed by gas. The gasin the gas seal is provided under pressure via inlet 15 to the gapbetween barrier member 12 and substrate W. The gas is extracted viaoutlet 14. The overpressure on the gas inlet 15, vacuum level on theoutlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow 16 inwardly that confines the liquid. The forceof the gas on the liquid between the barrier member 12 and the substrateW contains the liquid in a space 11. The inlets/outlets may be annulargrooves which surround the space 11. The annular grooves may becontinuous or discontinuous. The flow of gas 16 is effective to containthe liquid in the space 11. Such a system is disclosed in United Statespatent application publication no. US 2004-0207824, which is herebyincorporated by reference in its entirety. In an embodiment, the liquidconfinement structure 12 does not have a gas seal.

FIG. 6 illustrates a liquid confinement structure 12 which is part of aliquid supply system. The liquid confinement structure 12 extends aroundthe periphery (e.g. circumference) of the final element of theprojection system PS.

A plurality of openings 20 in the surface which in part defines thespace 11 provide the liquid to the space 11. The liquid passes throughopenings 29, 20 in side walls 28, 22 respectively through respectivechambers 24, 26 prior to entering the space 11.

A seal is provided between the bottom of the liquid confinementstructure 12 and a facing surface, e.g. the substrate W, or a substratetable WT, or both. In FIG. 6 a seal device is configured to provide acontactless seal and is made up of several components. Radiallyoutwardly from the optical axis of the projection system PS, there isprovided a (optional) flow control plate 51 which extends into the space11. The control plate 51 may have an opening 55 to permit flow liquidtherethrough; the opening 55 may be beneficial if the control plate 51is displaced in the Z direction (e.g., parallel to the optical axis ofthe projection system PS). Radially outwardly of the flow control plate51 on the bottom surface of the liquid confinement structure 12 facing(e.g., opposite) the facing surface, e.g., the substrate W, may be anopening 180. The opening 180 can provide liquid in a direction towardsthe facing surface. During imaging this may be useful in preventingbubble formation in the immersion liquid by filling a gap between thesubstrate W and substrate table WT with liquid.

Radially outwardly of the opening 180 may be an extractor assembly 70 toextract liquid from between the liquid confinement structure 12 and thefacing surface. The extractor assembly 70 may operate as a single phaseor as a dual phase extractor.

Radially outwardly of the extractor assembly 70 may be a recess 80. Therecess 80 is connected through an inlet 82 to the atmosphere. The recess80 may be connected via an outlet 84 to a low pressure source. Radiallyoutwardly of the recess 80 may be a gas knife 90. An arrangement of theextractor assembly, recess and gas knife is disclosed in detail inUnited States patent application publication no. US 2006/0158627incorporated herein in its entirety by reference.

The extractor assembly 70 comprises a liquid removal device, extractoror inlet such as the one disclosed in United States patent applicationpublication no. US 2006-0038968, incorporated herein in its entirety byreference. In an embodiment, the liquid removal device 70 comprises aninlet which is covered in a porous material 110 which is used toseparate liquid from gas to enable single-liquid phase liquidextraction. An under pressure in chamber 120 is chosen is such that themeniscuses formed in the holes of the porous material 110 preventambient gas from being drawn into the chamber 120 of the liquid removaldevice 70. However, when the surface of the porous material 110 comesinto contact with liquid there is no meniscus to restrict flow and theliquid can flow freely into the chamber 120 of the liquid removal device70.

The porous material 110 has a large number of small holes each with adimension, e.g. a width, such as a diameter, in the range of 5 to 50micrometers. The porous material 110 may be maintained at a height inthe range of 50 to 300 micrometers above a surface, such as a facingsurface, from which liquid is to be removed, e.g. the surface of asubstrate W. In an embodiment, porous material 110 is at least slightlyliquidphilic, i.e. having a dynamic contact angle of less than 90°,desirably less than 85° or desirably less than 80°, to the immersionliquid, e.g. water.

Although not specifically illustrated in FIG. 6, the liquid supplysystem has an arrangement to deal with variations in the level of theliquid. This is so that liquid which builds up between the projectionsystem PS and the liquid confinement structure 12 can be dealt with anddoes not escape. One way of dealing with this liquid is to provide alyophobic (e.g., hydrophobic) coating. The coating may form a bandaround the top of the liquid confinement structure 12 surrounding theopening and/or around the last optical element of the projection systemPS. The coating may be radially outward of the optical axis of theprojection system PS. The lyophobic (e.g., hydrophobic) coating helpskeep the immersion liquid in the space 11.

Another localized area arrangement is a fluid handling system whichmakes use of a gas drag principle. The so-called gas drag principle hasbeen described, for example, in United States patent applicationpublication nos. US 2008-0212046, US 2009-0279060 and US 2009-0279062.In that system the extraction holes are arranged in a shape which maydesirably have a corner. The corner may be aligned with a preferreddirection of movement, such as the stepping or the scanning direction.This reduces the force on the meniscus between two openings in thesurface of the fluid handing structure for a given speed in thepreferred direction compared to if the two outlets were alignedperpendicular to the preferred direction. However, an embodiment of theinvention may be applied to a fluid handling system which in plan hasany shape, or has a component such as the extraction openings arrangedin any shape. Such a shape in a non-limiting list may include an ellipsesuch as a circle, a rectilinear shape such as a rectangle, e.g. asquare, or a parallelogram such as a rhombus or a cornered shape withmore than four corners such as a four or more pointed star.

In a variation of the system of US 2008/0212046 A1, to which anembodiment of the present invention may relate, the geometry of thecornered shape in which the openings are arranged allows sharp corners(between about 60° and 90°, desirably between 75° and 90° and mostdesirably between 75° and 85°) to be present for the corners alignedboth in the scan and in the stepping directions. This allows increasedspeed in the direction of each aligned corner. This is because thecreation of liquid droplets due to an unstable meniscus, for example inexceeding a critical speed, in the scanning direction is reduced. Wherecorners are aligned with both the scanning and stepping directions,increased speed may be achieved in those directions. Desirably the speedof movement in the scanning and stepping directions may be substantiallyequal.

FIG. 7 illustrates schematically and in plan meniscus pinning featuresof a fluid handling system or of a liquid confinement structure 12having an extractor embodying the gas drag principle and to which anembodiment of the present invention may relate. The features of ameniscus pinning device are illustrated which may, for example, replacethe meniscus pinning arrangement 14, 15, 16 of FIG. 5 or at least theextractor assembly 70 shown in FIG. 6. The meniscus pinning device ofFIG. 7 is a form of extractor. The meniscus pinning device comprises aplurality of discrete openings 50. Each opening 50 is illustrated asbeing circular, though this is not necessarily the case. Indeed one ormore of the openings 50 may be one or more selected from: circular,elliptical, rectilinear (e.g. square, or rectangular), triangular, etc.and one or more openings may be elongate. Each opening has, in plan, alength dimension (i.e. in the direction from one opening to the adjacentopening) of greater than or equal to 0.2 mm, desirably greater than orequal to 0.5 mm or 1 mm, in an embodiment selected from the range of 0.1mm to 10 mm, in one embodiment selected from the range of 0.25 mm to 2mm. In an embodiment the width of each opening is selected from therange of 0.1 mm to 2 mm. In an embodiment the width of each opening isselected from the range of 0.2 mm to 1 mm. In an embodiment the lengthdimension is in the range of 0.2 mm to 0.5 mm, desirably in the range of0.2 mm to 0.3 mm.

Each of the openings 50 of the meniscus pinning device of FIG. 7 may beconnected to a separate under pressure source. Alternatively oradditionally, each or a plurality of the openings 50 may be connected toa common chamber or manifold (which may be annular) which is itself heldat an under pressure. In this way a uniform under pressure at each or aplurality of the openings 50 may be achieved. The openings 50 can beconnected to a vacuum source and/or the atmosphere surrounding the fluidhandling system (or confinement structure) may be increased in pressureto generate the desired pressure difference.

In the embodiment of FIG. 7 the openings are fluid extraction openings.Each opening is an inlet for the passage of gas, liquid, or a two phasefluid of gas and liquid, into the fluid handling system. Each inlet maybe considered to be an outlet from the space 11.

The openings 50 are formed in a surface of a fluid handling structure12. The surface faces the substrate W and/or substrate table WT, in use.In an embodiment the openings are in a flat surface of the fluidhandling structure 12. In an embodiment, a ridge may be present on thebottom surface of the substrate member. At least one of the openings maybe in the ridge. The openings 50 may be defined by needles or tubes. Thebodies of some of the needles, e.g., adjacent needles, may be joinedtogether. The needles may be joined together to form a single body. Thesingle body may form the cornered shape.

The openings 50 are the end of a tube or elongate passageway, forexample. Desirably the openings are positioned such that in use they aredirected, desirably face, to the facing surface, e.g. the substrate W.The rims (i.e. outlets out of a surface) of the openings 50 may besubstantially parallel to a top surface of a part of the facing surface.An elongate axis of the passageway to which the opening 50 is connectedmay be substantially perpendicular (within +/−45°, desirably within 35°,25° or even 15° from perpendicular) to the top of the facing surface,e.g., the top surface of the substrate W.

Each opening 50 is designed to extract a mixture of liquid and gas. Theliquid is extracted from the space 11 whereas the gas is extracted fromthe atmosphere on the other side of the openings 50 to the liquid. Thiscreates a gas flow as illustrated by arrows 100 and this gas flow iseffective to pin the meniscus 320 between the openings 50 substantiallyin place as illustrated in FIG. 7. The gas flow helps maintain theliquid confined by momentum blocking, by a gas flow induced pressuregradient and/or by drag (shear) of the gas (e.g., air) flow on theliquid.

The openings 50 surround the space to which the fluid handling structuresupplies liquid. The openings 50 may be distributed in an undersurfaceof the fluid handling structure. The openings 50 may be substantiallycontinuously spaced around the space (although the spacing betweenadjacent openings 50 may vary). In an embodiment of the presentinvention liquid is extracted all the way around the cornered shape andis extracted substantially at the point at which it impinges on thecornered shape. This is achieved because the openings 50 are formed allthe way around the space (in the cornered shape). In this way the liquidmay be confined to the space 11. The meniscus may be pinned by theopenings 50, during operation.

As can be seen from FIG. 7, the openings 50 are positioned so as toform, in plan, a cornered shape (i.e. a shape with corners 52). In thecase of FIG. 7 this is in the shape of a rhombus, desirably a square,with curved edges or sides 54. The edges 54, if curved, have a negativeradius. The edges 54 may curve towards the center of the cornered shapein areas away from the corners 52. An embodiment of the invention may beapplied to any shape, in plan, including, but not limited to the shapeillustrated, for example, a rectilinear shape, e.g. a rhombus, a squareor rectangle, or a circular shape, a triangular shape, a star shape, anelliptical shape, etc.

The cornered shape has principal axes 111, 121 aligned with the majordirections of travel of the substrate W under the projection system PS.This helps ensure that, below a critical scan speed, the maximum scanspeed is faster than if the openings 50 were arranged in a circularshape. This is because the force on the meniscus between two openings 50is reduced with a factor cos θ. Here θ is the angle of the lineconnecting the two openings 50 relative to the direction in which thesubstrate W is moving.

The use of a square cornered shape allows movement in the step andscanning directions to be at an equal maximum speed. This may beachieved by having each of the corners 52 of the shape aligned with thescanning and stepping directions 111, 121. If movement in one of thedirections, for example the scan direction is preferred to be fasterthan movement in the step direction then a rhombus shape could be used.In such an arrangement the primary axis of the rhombus may be alignedwith the scan direction. For a rhombic shape, although each of thecorners may be acute, the angle between two adjacent sides of therhombus, for example in the stepping direction, may be obtuse, i.e. morethan 90° (for example selected from the range of about 90° to 120°, inan embodiment selected from the range of about 90° to 105°, in anembodiment selected from the range of about 85° to 105°).

Throughput can be optimized by making the primary axis of the shape ofthe openings 50 aligned with the major direction of travel of thesubstrate (usually the scan direction) and to have a second axis alignedwith the other major direction of travel of the substrate (usually thestep direction). It will be appreciated that any arrangement in which isdifferent to 90° will give an advantage in at least one direction ofmovement. Thus, exact alignment of the principal axes with the majordirections of travel is not vital.

An advantage of providing the edges with a negative radius is that thecorners may be made sharper. An angle selected from the range of 75 to85° or even lower may be achievable for both the corners 52 aligned withthe scan direction and the corners 52 aligned with the step direction.If it were not for this feature then in order for the corners 52 alignedin both directions to have the same angle, those corners would have tohave 90°. If less than 90° were desired it would be necessary to selectone direction to have corners with less than 90° with the result thatthe other corner would have an angle of greater than 90°.

There may be no meniscus pinning features radially inwardly of theopenings 50. The meniscus is pinned between the openings 50 with dragforces induced by gas flow into the openings 50. A gas drag velocity ofgreater than about 15 m/s, desirably about 20 m/s is sufficient. Theamount of evaporation of liquid from the substrate may be reducedthereby reducing both splashing of liquid as well as thermalexpansion/contraction effects.

In an embodiment, at least thirty-six (36) discrete openings 50 eachwith a diameter of 1 mm and separated by 3.9 mm may be effective to pina meniscus. In an embodiment, one hundred and twelve (112) openings 50are present. The openings 50 may be square, with a length of a side of0.5 mm, 0.3 mm, 0.2 mm or 0.1 mm. The total gas flow in such a system isof the order of 100 l/min. In an embodiment the total gas flow isselected from the range of 70 l/min to 130 l/min.

Other geometries of the bottom of the fluid handling structure arepossible. For example, any of the structures disclosed in U.S. patentapplication publication no. US 2004-0207824 or U.S. patent applicationno. U.S. 61/181,158, filed on 26 May 2009, could be used in anembodiment of the present invention.

As can be seen in FIG. 7, relative to the space 11, one or more slits 61may be provided outside the openings 50. The slit 61 may besubstantially parallel to the lines joining the openings 50. In anembodiment the slit 61 may be a series of discrete apertures providedalong a side 54 of the shape. In use, the slit 61 is connected to anover pressure and forms a gas knife 60 surrounding the meniscus pinningdevice formed by openings 50.

The gas knife 60 in an embodiment of the invention functions to reducethe thickness of any liquid film left on a facing surface, such as thesubstrate W or substrate table WT. The gas knife 60 helps ensure thatthe liquid film does not break into droplets but rather the liquid isdriven towards the openings 50 and extracted. In an embodiment the gasknife 60 operates to prevent the formation of a film. To achieve this,it is desirable that the distance between the center lines of the gasknife and of the meniscus pinning openings 50 is in the range of from1.5 mm to 4 mm, desirably from 2 mm to 3 mm. The line along which thegas knife 60 is arranged generally follows the line of the openings 50so that the distance between adjacent ones of the openings 50 and theslit 61 of the gas knife 60 is within the aforementioned ranges.Desirably the line along which the gas knife 60 is arranged is parallelto the line of the openings 50. It is desirable to maintain a constantseparation between adjacent ones of the openings 50 and the slit 61 ofthe gas knife 60. In an embodiment this is desirable along the length ofeach center line of the gas knife. In an embodiment the constantseparation may be in the region of one of more corners of the liquidhandling device.

Localized area fluid handling systems such as those described above,with reference to FIGS. 2-7, can suffer from bubble inclusion into thespace 11. As can be seen, a meniscus 320 extends between the fluidhandling system 12 and the surface under the fluid handling system 12.This meniscus 320 defines the edge of the space 11. When the meniscus320 and a droplet collide on the surface, for example a droplet ofliquid which has escaped the space 11, a bubble of gas may be includedinto the space 11. Inclusion of a bubble into the space 11 isdetrimental because a bubble of gas can lead to an imaging error. Adroplet is usually left behind on the surface in one of at least threecircumstances; (a) when the liquid handling device is located over theedge of a substrate W when there is relative movement between the liquidhandling device and the substrate W; (b) when the liquid handling deviceis located over a step change in height of the facing surface facing theliquid confinement structure when there is relative movement between theliquid handling device and the facing surface; and/or (c) due to toohigh relative speed between the liquid handling device and the facingsurface, for example when the meniscus becomes unstable, e.g. byexceeding the critical scan speed of the facing surface. A bubble may beincluded at the meniscus 400 illustrated in FIGS. 5 and 6 extendingbetween the liquid confinement structure 12 and the projection systemPS. Here a bubble of gas could be created by liquid supplied from aliquid inlet (inlet 13 in FIG. 5 and inlets 20 in FIG. 6) on theradially inward facing surface of the liquid handling system 12entraining gas from between the projection system PS and the liquidhandling device 12.

Ways of dealing with the difficulty of bubble inclusion haveconcentrated on improving the confinement properties of a liquidconfinement structure 12. For example, the relative speed between theliquid confinement structure 12 and the facing surface has beendecreased in order to avoid spilling of liquid.

Very small bubbles of gas may dissolve in the immersion liquid beforethey reach the exposure area 328 (illustrated in FIG. 7) of the space11. An embodiment of the present invention uses the fact thatdissolution speed is dependent upon the type of the trapped gas and theimmersion liquid properties.

A bubble of carbon dioxide (CO₂) typically dissolves faster than abubble of air. A bubble of CO₂ which has a solubility fifty-five (55)times larger than that of nitrogen and a diffusivity of 0.86 times thatof nitrogen will typically dissolve in a time thirty-seven (37) timesshorter than the time for a bubble of the same size of nitrogen todissolve.

An experiment was carried out in which ultra pure water had beendegassed by boiling it. The water was then cooled and a vacuum of −950mbar was applied. Bubbles of ambient air and CO₂ were placed on the edgeof a substrate placed in the water. The bubbles had a size of between0.5 and 1 mm. After 30 seconds, the size of the bubbles of CO₂ hadreduced to between 0.1 mm and 0.3 mm and the bubbles of CO₂ were nolarger than 0.1 mm after 1 minute. During this time the size of thebubbles of air did not vary appreciably.

An analytical formula for the change in bubble diameter with time is:

$\frac{D_{bub}}{t} = \frac{{Sh} \cdot {Diff} \cdot {Sol} \cdot {{RT}\left( {P_{hyd} + \frac{4\; \sigma}{D_{bub}}} \right)}}{{\frac{1}{2}P_{hyd}D_{bub}} + {\frac{4}{3}\sigma}}$

where: R is the universal gas constant; T the temperature; Diff thediffusivity; Sol the solubility; t time; D_(bub) the diameter of thebubble; Sh the Sherwood number (kd/Diff, where: k is the mass transfercoefficient and d the characteristic dimension); P_(hyd) is thehydraulic pressure; and σ is the surface tension.

The equation shows that CO₂ bubbles with a diameter of lower than 1 mmwill dissolve in the time scale of 1 or 2 minutes. In comparison, abubble of nitrogen will dissolve in the hour time scale. This is inagreement with the above mentioned experiment.

Another analytical model relates dissolution time T to the bubblediameter, diffusivity, solubility, the universal gas constant andtemperature.

$\tau = \frac{D_{bub}^{2}}{6\; {{Sh} \cdot {Diff} \cdot {Sol} \cdot {RT}}}$

The second equation shows that a bubble of CO₂ of 1 mm diameter willdissolve in about 70 seconds compared to 110 seconds predicted by thefirst analytical model.

Therefore, the experimental result broadly agrees with the above twoanalytical models. Faster dissolution is achieved by a higher solubilityand/or a higher mass transfer coefficient. For a given set of flowconditions and geometry, to a first order approximation, the Sherwoodnumber is independent of the gas or liquid concerned. This shows thatthe mass transfer coefficient and diffusivity are substantiallyproportional. Therefore although the diffusivities on the top line ofthe first equation and on the bottom line of the second equation cancelout, because the mass transfer coefficient is proportional todiffusivity, a higher diffusivity leads to faster dissolution. Thereforesuitable gasses may have a higher solubility and/or a higherdiffusivity. Suitable gases may have a product of diffusivity andsolubility in the immersion liquid which is greater than that of air.

Using the results obtained by the analytical models it is possible todetermine about how quickly a bubble of a particular gas can be expectedto dissolve in liquid. A bubble included at the meniscus 320 may bestationary relative to the facing surface, and may be positioned on thesubstrate. The bubble may move through the space towards the exposurearea 328. In order for no imaging defects to occur, an included bubbledesirably dissolves before it reaches the exposure area 328 to beexposed by the projection beam B. For a given fluid handling system thedistance between the expected position of the meniscus 320 and theexposure area 328 is known. The distance of travel of the bubble may beequivalent to the distance of travel of the substrate W to travel underthe projection system PS from the position at which the bubble isincluded into the liquid to the position at which the bubble is in theexposure area. So for a high scan speed a bubble will need to dissolvefaster than for a slow scan speed, because the time taken for the bubbleto reach the exposure area 328 from the meniscus 320 will be less thanfor a lower scan speed. FIG. 8 shows calculations for a particulargeometry of fluid handling system with a distance between the expectedposition of the meniscus 320 and the exposure area 328 being about 30 mmfor various scan speeds. The maximum allowable size of a bubble (on they-axis) of carbon dioxide (squares) and of a bubble of nitrogen(diamonds) is plotted against scan speed (on the x-axis). As can beseen, the maximum allowable bubble diameter of a CO₂ bubble is muchgreater (approximately 8 times) than the maximum allowable bubblediameter of nitrogen.

If the bubble of gas is of a gas which has a high diffusivity,solubility or product of diffusivity and solubility in the immersionliquid, it will dissolve into the immersion liquid much faster accordingto the above two analytical models. Therefore, using an embodiment ofthe invention will reduce the number of imaging defects thereby allowinghigher throughput (e.g., higher speed of the substrate W relative to theliquid handling system 12) and lower defectivity.

Therefore, an embodiment of the present invention provides a gassupplying device configured to supply gas to a region (e.g. to a volume,or a towards an area) adjacent the space 11. In particular, gas isprovided such that it is present in the region adjacent to the meniscus320 extending between the facing surface and the liquid handling device12 and/or adjacent to the meniscus 400 extending between the liquidhandling device 12 and the projection system PS.

Gases which are suitable are, for example, those with solubilities (massof gas per unit mass of immersion liquid at a total pressure of 1 atm(sum of the partial pressures of gas and immersion liquid)) in theimmersion liquid (for example, water) of greater than 1×10⁻³ at 20° C.and 1 atm total pressure. Volume of gas rather than weight of gas may bemore important because a certain volume of gas rather than weight isneeded to fill the region adjacent the space. Therefore, the solubilitymay be better expressed in mols of gas per kg of liquid (i.e. inmol/kg). In that case the solubility should be greater than 5×10⁻³mol/kg, desirably greater than 10×10⁻³ mol/kg, 15×10⁻³ mol/kg, 20×10⁻³mol/kg or 25×10⁻³ mol/kg.

Gases which are suitable are, for example, those with diffusivities ofgreater than 3×10⁻⁵ cm² s⁻¹ at 20° and 1 atm total pressure. Thiscompares to that of air which is 2.3×10⁻⁵ cm² s⁻¹. Desirably thediffusivity is greater than 8×10⁻⁵, 1×10⁻⁴, or 5×10⁻⁴ cm² s⁻¹. Mostgasses have a diffusivity of between 1-2×10⁻⁵ cm² s⁻¹. Both oxygen andnitrogen have a diffusivity of 2.3×10⁻⁵ cm² s⁻¹ and carbon dioxide is1.6×10⁻⁵ cm² s⁻¹. Helium has a diffusivity of 3.8×10⁻⁵ cm² s⁻¹ (and asolubility of 1.6×10⁻⁶ kg/kg or 4×10⁻⁴ mol/kg). Hydrogen has adiffusivity of 5.8×10⁻⁵ cm² s⁻¹ (and a solubility of 1.6×10⁻⁶ kg/kg or8×10⁻⁴ mol/kg).

Particularly desirable are gases with solubilities of greater than1×10⁻³ kg/kg or 3×10⁻³ mol/kg at 20° C. and 1 atm total pressure and/ordiffusivities in the immersion liquid of greater than 3×10⁻⁵ cm² s⁻¹ at20° C. and 1 atm pressure. In an embodiment the gas is a gas which has aproduct of diffusivity and solubility greater than that of air. Forexample, the product of diffusivity and solubility should be greaterthan 1×10⁻⁹ cm² s⁻¹ (using a mass ratio for the solubility) or 2×10⁻⁸mol cm² s⁻¹ kg⁻¹ (using mol/kg for solubility). Desirably the product ofsolubility and diffusivity is greater than 5×10⁻⁹, 1×10⁻⁸ or 3×8⁻⁸ cm²s⁻¹ (using a mass ratio for the solubility) or 4×10⁻⁸, 10×10⁻⁸, 20×10⁻⁸,40×10⁻⁸ or 50×10⁻⁸ cm² s⁻¹ mol kg⁻¹ (using mol/kg for solubility). Anexample gas is carbon dioxide.

In an embodiment, gases with a product of solubility and diffusivitygreater than that of air (at 20° C. and 1 atm total pressure) are used.The solubility may be measured in kg/kg or in mol/kg. Gases with thoseproperties will dissolve in the immersion liquid faster than air therebyallowing a higher scan speed to be used without risk of bubbles includedat the meniscus 320, 400 from still being present in the exposure areaat exposure time.

An example gas is carbon dioxide which may be desirable because it isreadily available and may be used in immersion systems for otherpurposes. Carbon dioxide has solubility in water at 20° C. and 1 atmtotal pressure of 1.69×10⁻³ kg/kg or 37×10⁻³ mol/kg. Other suitablegases may be chlorine (7.0×10⁻³ kg/kg or 98×10⁻³ mol/kg), hydrogensulphide (3.85×10⁻³ kg/kg or 113×10⁻³ mol/kg), hydrogen chloride (0.721kg/kg or 19753×10⁻³ mol/kg), ammonia (0.531 kg/kg or 31235×10⁻³ mol/kg)or sulphur dioxide (0.113 kg/kg or 1765×10⁻³ mol/kg). Some of thosegases may have one or more disadvantages. For example, some of thosegases may react with components in the immersion lithographic apparatusand/or may be poisonous and may therefore be harder to handle and lessdesirable than carbon dioxide. Any non-reactive gas which readilydissolves in immersion liquid is suitable.

These gases used in an embodiment of the invention contrast to oxygenand nitrogen which have solubilities in water of 4.34×10⁻⁵ kg/kg or1.36×10⁻³ mol/kg and 1.90×10⁻⁵ kg/kg or 0.68×10⁻³ mol/kg at 20° C. and 1atm total pressure respectively. Either of oxygen or nitrogen or air, ofwhich those two gases form the predominant part, are therefore unlikelyto dissolve before reaching the exposure area 325 of the space 11.

The gas supplying device supplies gas with a solubility in immersionliquid of greater than 1×10⁻³ kg/kg or 5×10⁻³ mol/kg at 20° C. and 1 atmtotal pressure to the exclusion of other gases. So any gas exiting thegas supply device may have a solubility of greater than 1×10⁻³ kg/kg or5×10⁻³ mol/kg. Such a gas supplying device is therefore distinguishablefrom a gas supplying device supplying air (which includes carbondioxide), because air includes oxygen and nitrogen which have lowersolubilities than 1×10⁻³ kg/kg or 5×10⁻³ mol/kg.

An embodiment of the present invention herein described may form a CO₂atmosphere around the meniscus 320, 400 of immersion liquid so that anyinclusion of gas into the immersion liquid creates a gas inclusion whichdissolves in the immersion liquid. Dissolving CO₂ in the immersionliquid prior to supplying the immersion liquid to the space (for exampleto change the resistivity of the immersion liquid) provides the CO₂ as asolute and not a gas. Supplying a solute of CO₂ would not work in thesame way as an embodiment of the present invention because the CO₂ issupplied in the immersion liquid. In providing the CO₂ as a solute inthe immersion liquid instead of a gaseous atmosphere in the region ofthe meniscus, the CO₂ has already dissolved in the liquid in the space.The CO₂ is not present in the gas of an included bubble, so the presenceof the CO₂ in the immersion liquid would not facilitate the reduction inthe size of the included bubble. Such an arrangement could be consideredto be contrary to the way an embodiment of the present invention works.

In an embodiment the immersion liquid is degassed prior to beingsupplied to the space 11. In an embodiment, minimal, desirably no, gasis dissolved in the immersion liquid after degassing and prior to beingsupplied to the space 11. In particular, no component existsdeliberately to dissolve gas in the immersion liquid between theimmersion liquid being degassed and being supplied to the space 11.Previously it has been suggested to dissolve carbon dioxide in immersionliquid prior to providing it to the space 11 in order to change theacidity or electrical conductivity of the immersion liquid, for exampleto help prevent corrosion of one or more components which contact theimmersion liquid. However, addition of carbon dioxide need only be addedsufficiently to prevent corrosion, below the concentration of carbondioxide at which the effect of an embodiment of the present invention onan included bubble is not appreciable. In an embodiment of the presentinvention, a high concentration of carbon dioxide dissolved in theimmersion liquid may be undesirable because deliberately dissolving gasinto the immersion liquid above a certain concentration will reduce thesolubility of that gas in immersion liquid. The presence of the gas insolution (at least above a certain threshold) could thereby reduce thelikelihood that the gas of an included bubble will dissolve quicklyenough to help reduce, if not avoid, the chance of an imaging defect.

In an embodiment, a gas atmosphere is created at the liquid meniscus320, 400. That may include enclosing the exposure area of the immersionlithographic apparatus with gas. The exposure area is the entire areasurrounding the end of the projection system PS. In an embodiment, theentire inside of the apparatus has the gas supplied to it. In anembodiment, a local supply of gas to the meniscus 320, 400 is provided.For example, separate openings 200, 201 can be provided in the barriermember 12 to provide gas to the meniscus 320, 400. In an embodiment, thegas may be provided through a gas knife, as described below. In anembodiment, gas may be supplied to the region of the barrier member, forexample as a purging gas.

Typically the gas supplying device comprises a source of gas and anopening which is connected to the source of gas via a conduit. In anembodiment the gas is provided in a fluid handling system such as thatillustrated in FIG. 7 without a gas knife 60, so that a gas atmosphere600 of a high solubility gas surrounds the entire liquid handling device12. The liquid confinement structure 12 is in a gas atmosphere 600, forexample shrouded in a gas cloud, supplied in the region of the fluidhandling system, for example as a purging gas. The gas could be providedthrough a gas opening 500 separate from (e.g. adjacent to) the liquidconfinement structure 12. The opening 500 could be at the end of aconduit 510 which extends between the gas opening 500 and the source ofgas 520. The gas opening 500 may be one or more openings around theperiphery of the liquid confinement structure 12. The opening maysurround the liquid confinement structure 12. The same or a similarsystem could be used in the other embodiments, particularly those ofFIGS. 2 to 4.

In an embodiment, the opening for high solubility gas may be formed inthe fluid handling system 12. The gas opening 200, 201 may be connectedto the source of gas 520. For example, the gas opening may be anintegral opening 200 formed in the surface of the liquid confinementstructure 12, as shown in FIG. 6. The integral opening 200 is radiallyoutward of the meniscus, and may be radially outward of the extractor70, with respect to the optical axis of the projection system PS. Gaswith high solubility in immersion liquid exiting the integral opening(or outlet) 200 may thereby be adjacent the meniscus 320. Gas exitingthe integral opening 200 may be included into the immersion liquid inthe space 11 in a gas bubble upon collision of a liquid droplet with themeniscus 320. Because the gas is easily absorbed into the immersionliquid, it will desirably be absorbed into the immersion liquid beforereaching the optical path in the space 11. An integral opening 200 suchas that illustrated in FIG. 6 could be in any type of fluid handlingsystem 12, for example, at a position adjacent an extractor. In FIG. 6is a further opening 201 to provide gas adjacent the meniscus 400extending between the liquid confinement structure 12 and the projectionsystem PS. The further opening 201 is radially outwardly of the expectedposition of the meniscus 400.

Pre-existing gas supplying features, such as a gas knife, shown in FIGS.5, 6 and 7 could be used in the gas supplying device to supply the gaswith high solubility in immersion liquid described herein. Gas suppliedout of opening 15 in FIG. 5 could consist of the gas with a solubilityin the immersion liquid of greater than 1×10⁻³ kg/kg or 5×10⁻³ mol/kg at20° C. and 1 atm total pressure. The gas used in the gas knife 90 ofFIG. 6 and the gas knife 60 of FIG. 7 could consist of a gas with asolubility in immersion liquid of greater than 1×10⁻³ kg/kg or 5×10⁻³mol/kg at 20° C. and 1 atm total pressure. In each case, the opening 15,90, 60 could be connected to the source of gas 520, Thus, existingdesigns of fluid handling system 12 could be used. In using an existingdesign of fluid handling system 12, the size of the system 12 can atleast be maintained if not minimized.

The gas is supplied in such a way that environmental gas (e.g. air) islargely expelled from the environment of the liquid/gas separation line(e.g. at meniscus 320, 400). The gas may be supplied at or radiallyoutward of the meniscus 320, 400. In an embodiment, the gas is suppliedas a purging gas to shield the meniscus from the ambient environmentalgas. In an embodiment, the gas is supplied to confine the liquid in thereservoir or immersion space. The gas may be supplied between the liquidhandling system and a facing surface (for example, a substrate tableand/or a substrate) to form a seal therebetween. The supplied gas mayform a barrier between the meniscus of the immersion liquid and theambient atmosphere of, for example, air.

The atmosphere to which meniscus 320, 400 is exposed is mainly thesupplied gas. Therefore, in the absence of bubble formation, gasdissolves into the immersion liquid at the meniscus 320, 400. Over timethe concentration of the supplied gas may increase. Liquid at themeniscus is consequently affected most by the supplied gas. Theincreased concentration of the supplied gas may affect opticalproperties of the immersion liquid, for example its refractive index.However, continual extraction of liquid from the space 11 at themeniscus helps prevent the liquid radially inward of the meniscus frombeing substantially affected by the increased concentration of the gas.

However, any bubble which is formed at the meniscus, for example oncollision with a droplet, is likely to include a gas bubble at leastlargely of the supplied gas. The bubble, as it contains the suppliedgas, readily dissolves in the immersion liquid, beyond the region ofextraction of, for example, outlet 14, openings 50, or extractor 70.Because the bubble desirably dissolves before it reaches the exposurearea 325, i.e. the path of the projection beam through the space 11,most of the gas of the bubble dissolves in the immersion liquid beforeit reaches the exposure area 325. Since most of the liquid in the pathof the bubble is extracted near the meniscus, it is likely that theliquid in which the supplied gas is dissolved, is extracted before itsignificantly affects the optical properties of the immersion liquid inthe space.

By using gaseous CO₂ the problem associated with the meniscus 320colliding with a droplet of liquid may be reduced if not alleviated.Typically a droplet of 300 micrometers would produce a bubble of 30micrometers in diameter (i.e. a tenth the size). Such a bubble of carbondioxide would usually dissolve in the immersion liquid before reachingthe exposure area. (Note that a droplet of such a size may cause one ormore other problems). Therefore the problems caused by a droplet wouldbe less significant. The immersion system would be more tolerant ofinteracting with immersion liquid which had escaped from the space.

A re-cycling device 650 may be used to collect any undissolved gas froma gas supplying device and return the undissolved gas to the gas source520 of the gas supplying device for re-use. It should be noted that afluid handling system applying the gas drag principle, as described withreference to FIG. 7, is likely to use a large quantity of gas from a gassupplying device as compared to a liquid supply device using a singlephase extractor such described with reference to FIG. 6. Therefore, arecycling device 650 may be particularly advantageous for use with anfluid handling system which applies the gas drag principle.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application. For example, anembodiment of the invention could be applied to the embodiments of FIGS.2 to 4.

In an embodiment, there is provided an immersion lithographic apparatuscomprising: a fluid handling system configured to confine immersionliquid to a localized space between a final element of a projectionsystem and a substrate and/or table; and a gas supplying deviceconfigured to supply gas with a solubility in the immersion liquid ofgreater than 5×10⁻³ mol/kg at 20° C. and 1 atm total pressure to aregion adjacent the space.

In an embodiment, the gas supplying device comprises a source of gaswith a solubility in immersion liquid of greater than 5×10⁻³ mol/kg at20° C. and 1 atm total pressure.

In an embodiment, there is provided an immersion lithographic apparatuscomprising: a fluid handling system configured to confine immersionliquid to a localized space between a final element of a projectionsystem and a substrate and/or table; and a gas supplying deviceconfigured to supply gas with a diffusivity in the immersion liquid ofgreater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atm total pressure to aregion adjacent the space.

In an embodiment, the gas supplying device comprises a source of gaswith a diffusivity in immersion liquid of greater than 8×10⁻⁵ cm² s⁻¹ at20° C. and 1 atm total pressure.

In an embodiment, there is provided an immersion lithographic apparatuscomprising: a fluid handling system configured to confine immersionliquid to a localized space between a final element of a projectionsystem and a substrate and/or table; and a gas supplying deviceconfigured to supply gas with a product of diffusivity and solubility inthe immersion liquid of greater than that of air at 20° C. and 1 atmtotal pressure to a region adjacent the space.

In an embodiment, the gas supplying device comprises a source of gaswith a product of diffusivity and solubility in immersion liquid ofgreater than 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm total pressure.

In an embodiment, the source of gas is a source of carbon dioxide. In anembodiment, the gas supplying device comprises an opening through whichgas is supplied. In an embodiment, the gas supply device is configuredto supply gas to fill an exposure area of the immersion lithographicapparatus with the gas. In an embodiment, the opening is adjacent thefluid handling system. In an embodiment, the opening is positioned tosupply the gas to a local area adjacent the localized space. In anembodiment, the fluid handling system comprises a liquid confinementstructure. In an embodiment, the gas supplying device, desirably theopening, is positioned to shroud the liquid confinement structure in thegas. In an embodiment, the gas supplying device, desirably the opening,is positioned to provide an atmosphere consisting of the gas in whichthe liquid confinement structure is situated. In an embodiment, the gassupplying device is configured to supply gas to a region adjacent ameniscus extending between the liquid confinement structure and thesubstrate and/or table and/or between the liquid confinement structureand the projection system. In an embodiment, the liquid confinementstructure includes an extractor. In an embodiment, the extractorcomprises a porous member. In an embodiment, the extractor comprises aplurality of openings in the liquid confinement structure. In anembodiment, the gas supplying device comprises an opening in the liquidconfinement structure radially outwardly of the extractor. In anembodiment, the opening forms a gas knife or gas seal. In an embodiment,the immersion lithographic apparatus further comprises a recyclingdevice to collect any undissolved gas from the gas supplying device andreturn the undissolved gas to the gas supplying device for re-use.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a localized space between a final elementof a projection system and a substrate; and providing to a regionadjacent to the space a gas with a solubility in the immersion liquid ofgreater than 5×10⁻³ mol/kg at 20° C. and 1 atm total pressure.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a localized space between a final elementof a projection system and a substrate; and providing to a regionadjacent to the space a gas with a diffusivity in the immersion liquidof greater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atm total pressure.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a localized space between a final elementof a projection system and a substrate; and providing to a regionadjacent to the space a gas with a product of diffusivity and solubilityin the immersion liquid of greater than that of air at 20° C. and 1 atmtotal pressure.

In an embodiment, the provided gas expels other gas from the area. In anembodiment, the gas is carbon dioxide.

In an embodiment, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table, and comprising agas supplying device configured to supply gas with a solubility in theimmersion liquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm totalpressure to a region adjacent the space.

In an embodiment, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table; and comprising agas supplying device configured to supply gas with a diffusivity in theimmersion liquid of greater than 3×10⁻⁵ cm² s⁻¹ at 20° C. and 1 atmtotal pressure to a region adjacent the space.

In an embodiment, there is provided a fluid handling system for animmersion lithographic apparatus, the fluid handling system configuredto confine immersion liquid to a localized space between a final elementof a projection system and a substrate and/or table; and comprising agas supplying device configured to supply gas with a product ofdiffusivity and solubility in the immersion liquid of greater than thatof air at 20° C. and 1 atm total pressure to a region adjacent thespace.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

Any controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate and/or substrate table so thatsubstantially the entire uncovered surface of the substrate table and/orsubstrate is wetted. In such an unconfined immersion system, the liquidsupply system may not confine the immersion liquid or it may provide aproportion of immersion liquid confinement, but not substantiallycomplete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more fluid openingsincluding one or more liquid openings, one or more gas openings or oneor more openings for two phase flow. The openings may each be an inletinto the immersion space (or an outlet from a fluid handling structure)or an outlet out of the immersion space (or an inlet into the fluidhandling structure). In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-21. (canceled)
 22. A system, comprising: a movable table; aprojection system configured to project a beam of radiation onto asubstrate, the projection system comprising an optical element nearestthe table; a fluid handling system configured to confine immersionliquid to a localized liquid space between the element of the projectionsystem and the table, the fluid handling system comprising a liquidconfinement structure arranged to define a gap between a boundingsurface of the liquid confinement structure and an opposing surface; anda gas supply device configured to supply gas from a gas source to aregion adjacent the liquid space, the gas having a solubility in theimmersion liquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm totalpressure or a product of diffusivity and solubility in immersion liquidof greater than 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm totalpressure, and the gas supply device comprising a first orifice, outwardof the localized liquid space and facing the opposing surface,configured to supply the gas to the gap; and a second orifice configuredto supply a fluid different than the gas, the second orifice locatedoutward, relative the localized liquid space, of the first orifice andfacing the opposing surface.
 23. The system of claim 22, wherein theopposing surface comprise a surface of the table and wherein the firstand second orifices are in the bounding surface of the liquidconfinement structure facing the table surface.
 24. The system of claim22, wherein the gas comprises carbon dioxide.
 25. The system of claim22, further comprising a recycling device configured to collect the gasthat has not become incorporated into the immersion liquid and providesuch gas for re-use.
 26. The system of claim 22, wherein the gas has theproduct of diffusivity and solubility in immersion liquid of greaterthan 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm total pressure.
 27. Thesystem of claim 22, wherein the gas has the solubility in the immersionliquid of greater than 5×10⁻³ mol/kg at 20° C.
 28. The system of claim22, wherein the first and/or second orifices are positioned so that thegas substantially surrounds the localized liquid space and substantiallyseparates the localized liquid space from a different ambient gasatmosphere that surrounds the localized liquid space and comes intocontact around the localized liquid space with the gas.
 29. A system,comprising: a fluid handling system configured to confine immersionliquid to a localized liquid space between an optical element of aprojection system and a table, the fluid handling system comprising aliquid confinement structure arranged to define a gap between a boundingsurface of the liquid confinement structure and an opposing surface; anda gas supply device configured to supply gas from a gas source to aregion adjacent the liquid space, the gas having a solubility in theimmersion liquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm totalpressure or a product of diffusivity and solubility in immersion liquidof greater than 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm totalpressure, and the gas supply device comprising a first orifice, outwardof the localized liquid space and facing the opposing surface,configured to supply the gas to the gap; and a second orifice configuredto supply a fluid different than the gas, the second orifice locatedoutward, relative the localized liquid space, of the first orifice andfacing the opposing surface.
 30. The system of claim 29, wherein theopposing surface comprise a surface of the table and wherein the firstand second orifices are in the bounding surface of the liquidconfinement structure facing the table surface.
 31. The system of claim29, wherein the gas comprises carbon dioxide.
 32. The system of claim29, further comprising a recycling device configured to collect the gasthat has not become incorporated into the immersion liquid and providesuch gas for re-use.
 33. The system of claim 29, wherein the gas has theproduct of diffusivity and solubility in immersion liquid of greaterthan 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm total pressure.
 34. Thesystem of claim 29, wherein the gas has the solubility in the immersionliquid of greater than 5×10⁻³ mol/kg at 20° C.
 35. A devicemanufacturing method, comprising: projecting a beam of radiation throughan immersion liquid in a localized space between an optical element of aprojection system and a substrate, onto the substrate; confining theimmersion liquid to the localized liquid space using a liquidconfinement structure defining a gap between a bounding surface of theliquid confinement structure and an opposing surface; providing gas froma first orifice to the gap and to a region adjacent to the immersionliquid in the localized space, wherein the gas has a solubility in theimmersion liquid of greater than 5×10⁻³ mol/kg at 20° C. and 1 atm totalpressure or a product of diffusivity and solubility in immersion liquidof greater than 2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm totalpressure and wherein the first orifice is outward of the localizedliquid space and faces the opposing surface; and supplying a fluiddifferent than the gas from a second orifice, the second orifice locatedoutward, relative the localized liquid space, of the first orifice andfacing the opposing surface.
 36. The method of claim 35, wherein the gascomprises carbon dioxide.
 37. The method of claim 35, wherein the gashas the solubility in the immersion liquid of greater than 5×10⁻³ mol/kgat 20° C.
 38. The method of claim 35, wherein the gas has the product ofdiffusivity and solubility in the immersion liquid of greater than2×10⁻⁸ cm² s⁻¹ mol kg⁻¹ at 20° C. and 1 atm total pressure.
 39. Themethod of claim 35, further comprising recycling the gas that has notbecome incorporated into the immersion liquid for re-use.
 40. A devicemanufacturing method, comprising: projecting a beam of radiation throughan immersion liquid in a localized space between an optical element of aprojection system and a substrate, onto the substrate; confining theimmersion liquid to the localized liquid space using a liquidconfinement structure defining a first gap between the liquidconfinement structure and the projection system, or defining a secondgap between the liquid confinement structure and the table, or definingboth the first and second gaps; and providing gas from a gas sourcethrough one or more openings to the first and/or second gaps and to aregion adjacent to the immersion liquid in the localized space, the gashaving a solubility in the immersion liquid of greater than 5×10⁻³mol/kg at 20° C. and 1 atm total pressure or a product of diffusivityand solubility in immersion liquid of greater than 2×10⁻⁸ cm² s⁻¹ molkg⁻¹ at 20° C. and 1 atm total pressure and the one or more openingsbeing separate from the liquid confinement structure and positioned toprovide the gas such that the gas substantially surrounds the localizedliquid space and substantially separates the localized liquid space froma different ambient gas atmosphere that surrounds the localized liquidspace and comes into contact around the localized liquid space with thegas.
 41. The method of claim 40, wherein the gas comprises carbondioxide.
 42. The method of claim 40, comprising providing the gas sothat at least an exterior peripheral surface of the liquid confinementstructure is shrouded in the gas.